Electrical connections



Aug. 7, 1962 J. w. ALLEN ETAL 3,048,650

ELECTRICAL. CONNECTIONS Filed Oct. 17, 1958 m E 5 W: 1 (\*Q\\\\ INVENTOR.

JOHN h). RLLEN B DONALD E LERCH YGEORGE LAZIEGLER IR.

United States Patent Ofifice 3,048,650 Patented Aug. 7, 1962 3,048,650 ELECTRICAL CONNECTIONS John W. Allen, Donald P. Lerch, and George W. Ziegler,

Jr., Carlisle, Pa., assignors to AMP Incorporated, Harrisburg, Pa.

Filed Oct. 17, 1958, Ser. No. 767,878 Claims. (Cl. 17490) The use of electrical connectors having ferrule-forming portions which are U-shaped in cross-section for forming electrical connections to electrical conductors is now widespread, various methods of folding the arms of the connectors about the conductors being used. Such connectors have numerous advantages but suffer from the substantial disadvantage that no entirely satisfactory means of pre-insulating them has heretofore been found. Where pre-insulation has been required it has been necessary to use closed barrel type connectors.

Among the objects of this invention are the provision of a pre-insulated strip of electrical connectors, a blank for making the connectors, a method of crimping the connectors and a pre-insulated electrical connection. Other objects will become apparent hereinafter.

A pre-insulated strip of connectors according to this invention comprises a U-shaped strip of a linear polyester having one arm of the U longer than the other, the inside edge of the longer arm and the outside edge of the shorter arm being chamfered, the strip carrying a coating of a heat and pressure-sensitive adhesive on its inside surface and having U -shaped ferrule-forming portions of electrical connectors sticking to the inside surface at regular intervals. The preferred linear polyester is polyethylene therephthalate and in particular the material sold by E. I. Dupont de Nemours and Company Inc. under the registered trademark Mylar. We have found that the linear polyesters are the only plastic insulating materials that are satisfactory; they combine good mechanical properties with excellent electrical properties.

In accordance with the invention, a U-shaped ferruleforming portion of an electrical connector stuck to the inside surface of a U-shaped strip of a linear polyester, the arms of the polyester strip being of unequal length, the remainder of the inside surface having a coating of a heat and pressure-sensitive adhesive is crimped about an electrical conductor lying within the U. According to this feature the connector assembly is forced by means of a substantially plane anvil into a semi-cylindrical, heated, die so that the arms of the connector and strip are folded about the conductor and compressed together to give a connection substantially D-shaped in cross-section and substantially voidless, the shorter arm of the strip being gripped between the arms of the connector and the longer arm being stuck to the shorter arm by the heat from the die. Advantageously there is a series of connectors supported on a unitary continuous strip of linear polyester which is fed to present the connectors one by one to the die and anvil and in which each connector assembly is disconnected from the continuous strip by severing the strip while the connector is being applied to the conductor.

An electrical connection between a ferrule of an electrical connector and an electrical conductor lying within the ferrule forms a still further feature of the invention, according to which the connection is substantially D- shaped and substantially voidless in cross-section and the curved part of the connection has a longitudinal slit in which is held one side of a strip of a linear polyester. This strip is wrapped around the connector ferrule and overlaps itself to provide a continuous insulating sheath in surrounding relationship to the ferrule, and the other end of it overlapping the strip and sticking to it. Now,

it is clearly desirable that the outer layer of insulation must not be ruptured during the crimping operation and it has been found that rupturing is particularly liable to occur when the ferrule-forming portion of the connector is made, as is common, from a substantially rectangular plane blank, which is bent up into a U-shape in crosssection and presents a substantially rectangular side elevation. The reason for this is apparently the extrusion of the metal in the crimping operation which forms protuberances at each end of the edges of the arms of the connector; these protuberances rip and rupture the insulation. By making the connector from a circular blank we find that we are able to avoid this rupturing and at the same time achieve more than mere point to point contact of the curved arms of the connector, because of the extrusion of metal into the angles between the two arms. The ferrule-forming portion formed from a circular blank will be U-shaped in cross-section and its side elevation a segment of a circle.

The invention will now be described in greater detail and by way of example with reference to the accompanying drawings; it should be clearly understood that these drawings are given purely by way of example and not limitation and that various modifications, alterations and variations can be made to the illustrated embodiments within the scope of this invention. In the drawings:

FIGURE 1 is a perspective view of a strip of preinsulated connectors;

FIGURE .2 is a plan view of a blank for making the connectors shown in FIGURE 1;

FIGURE 3 is a section on the line 3-3 of FIGURE 2;

FIGURE 4 is a perspective view of a connection made with a connector from the strip of FIGURE 1;

FIGURE 5 is a section on the line 55 of FIGURE 2;

FIGURES 6 to 8 are partial sections showing stages in the crimping of a connection; and

FIGURES 9 and 10 are perspective views of alternative embodiments.

Referring first to FIGURE 1 a strip 2 of polyethylene terephthalate is U-shaped in cross-section. One arm 4 of the U is longer than the other arm 6. The inside edge of the arm 4 is chamfered at 8 and the outside edge of the arm 6 is chamfered at 10. The inside surface of the strip 2 has a coating of a pressure sensitive and heat curable adhesive. At regular intervals along the length of the strip 2 connectors 12 are stuck by means of the adhesive. The connectors are applied to the strip with heat and pressure. Each connector is made from a circular blank as shown in FIGURES 2 and 3.

The blanks are formed by a progressive die forming operation from a strip of brass, the final stage being the stamping of the circular blank from the strip. Each blank 14 has five parallel grooves 16 running across a central plateau 17 from which the blank tapers down gradually to its edges, which are thinner than the centre.

The blanks are formed up into U-shaped cross-section with the grooves 16 running at right angles to the axis of the U, before they are stuck to the strip 2.

The arms 4 and 6 of the strip 2 have slits 18 at regular intervals between the connectors .12 to enable the strip to be handled with greater ease and to be Wound up on reels. The slits 1S are of such a depth that they leave a connecting link between the units of the strip which is narrow enough to permit coiling but wide enough to prevent accidental breaking of the strip.

The connectors illustrated in FIGURE 1 are used for splicing two or more conductors together end to end or for joining two or more conductors together at points intermediate to their ends or for similar purposes. FIG- URES 4 and 5 illustrate a splice connection between two insulated stranded conductors 20 and 22. The two conductors lie side by side in the ferrule 24 formed by folding the arms of the connector 12 and the arms 4 and 6 of the strip about the conductors. The arms 4 and 6 are also curled around the insulation of the conductors 20 and 22 and form insulation supports 26.

The operation of the crimping process and the detailed construction of the connection will be apparent from FIG- URES 5 to 8. In FIGURES 6 to 8 a connector is in position on an anvil 28 which has a substantially plane upper surface. The anvil cooperates with a semi-circular die 36, having parallel lead-in surfaces 32 tangenial to the curved die surface. As the anvil 28 forces the connector into the semi-circular die the arms of the insulation are curled into the position shown in FIGURE 7; in this position by virtue of the chamfered edges 8 and 10 the longer arm 4 slides over the shorter arm 6. Continued forcing of the connector into the die 30 causes the shorter arm 6 to be gripped between the arms of the connector while the longer arm is forced to overlap the shorter arm.

The die 30 is heated, for example by an electrical heating element, not shown, mounted directly above the die cavity. The heat of the die activates the adhesive coating on the inner side of the arms 6 and 4, and sticks the insulation to itself, to the conductor where the shorter arm 6 enters the ferrule and to the insulation on the con ductors. The resulting connection is substantially D- shaped in cross-section and is forged to a substantially voidless connection. Preferably, the crimping operation is effected in two stages. The connector is compressed tightly around the conductors in a first stage and the pressure is then reduced while maintaining the connection in the die. This permits complete softening of the adhesive and ensures good sticking of the insulating material without the danger of extruding it from between the die and anvil.

The grooves 16 running across the connector assist in the gripping of the conductors and contribute to the tensile strength of the connection.

As the connector is applied to the conductors a shear blade removes the connector from the strip by cutting the link joining it to the next connector in the strip. The strip is then advanced another unit into position on the anvil for making the next connection.

In the connector shown in FIGURES 1 to 8 the connector is formed solely by the ferrule-forming portion and the connector is useful only for making splices. The invention is not, however, limited to this construction of connector. For example, the connector may have a ring tongue as shown in FIGURE 9. In the connector illustrated a ferrule-forming portion 34 is similar in construction to the connector 12, the base of the U being extended to form part of a ring-tongue 36. The strip of linear polyester again is coated with an adhesive and the con nectors stuck to it, but in this case the link joining two connectors is formed by one arm 38 (in this case the longer arm). Each connector is removed from the strip during the crimping operation by severing along the dotted lines 40.

FIGURE 10 shows a further embodiment in which the ferrule forming portions 12 are integral with rings 42 attached to each other in side by side relationship by means of slugs 44. In crimping terminals of this type onto wires, an automatic feeding means for the strip is advantageously provided to feed the terminal to a position beneath the crimping press.

While the invention has been herein disclosed with reference to a U-shaped ferrule adapted to be crimped onto a stripped wire, it will be apparent that the invention is also applicable to insulated wires, particularly Wires having one or more strands insulated with thin coverings of insulation such as varnish. In the latter case, the serrations 16 will serve the function of penetrating the varnish to establish electrical contact with the conductor as is known to the art.

It should also be mentioned that a connector in accordance with the invention need not necessarily be circular shown in the drawing although the circular blank shown presents substantial advantages in the manufacturing process. It is, however, highly desirable that the longitudinal edges of the connector be chamfered as shown and that these longitudinal edges be rounded, i.e. the U-shaped connector should offer as a sector of a circle in side elevation. Thus, a connector in accordance with the invention can be formed from an oval-shaped, or a rectangle whose ends have been rounded into sectors, rather than a round blank with the curved edges only having a chamfer.

We claim:

1. A U-shaped sheet of a linear polyester having one arm of the U longer than the other, at least one of said arms being chamfered along its longitudinal edge, said sheet carrying a coating of a heat-and-pressure sensitive adhesive on its surface within the U, at least one electrical connector of U-shaped cross section disposed in said sheet and adhering thereto with its arms parallel to the arms of said sheet, the side edges of the arms of said connector being rounded at their extremities and the edge portions of said arms of said connector having a tapered cross section, and said arms of said connector being devoid of sharp corners.

2. A strip of polyethylene terephthalate U-shaped in cross-section and having one arm of the U longer than the other, the inside edges of the longer arm and the outside edge of the shorter arm being chamfered, the strip having a coating of a heat-andpressure-sensitive adhesive on its inside surface and having electrical connectors sticklng to the inside surface of the strip, each electrical connector having a ferrule-forming portion U-shaped in cross-sectlon to conform with the strip and its side elevation being a segment of a circle. 3. A blank for making an electrical connector including as a ferrule-forming portion a circular disc of metal with its edge thinner than its centre and which tapers gradually from a central plateau outwards and has a senes of parallel grooves across the central plateau.

4. A crimped electrical connection between a ferrule of an electrical connector and an electrical conductor lying within the ferrule, the connection being substantially D-shaped and substantially voidless in cross section in which the curved part of the ferrule has a longitudinal seam in which is held one end of a strip of a linear polyester, the strip surrounding the ferrule and stuck to said ferrule, and the other end of said strip overlapping said one end and sticking to said one end, said ferrule having been formed from a circular blank and the edges of the curved part of said ferrule tapering towards said seam.

5. A method of making an electrical connection between two electrical conductors which comprises placing the conductors within a U-shaped electrical connector stuck to the inside surface of a U-shaped strip of a linear polyester with a heat-and-pressure-sensitive adhesive, and remalnder of the inside surface having a coating of the adhesive, the strip having one arm longer than the other and the edge of the longer arm of the strip being chamfered on its inside surface and the edge of the shorter arm be ng chamfered on its outside surface, said method comprrsmg the further steps of applying heat and pressure to curl the arms of said strip to position the shorter one of said arms under the longer one of said arms, thereafter further curling said arms and additionally curling the sides of said electrical connector towards each other until the sides of said connector grip the shorter arm of said strip and the longer arm of said strip is wrapped around the joint formed by the sides of said connector and overlaps the shorter arm of said strip, and then reducing the pressure applied to said connector and continuing to apply heat thereto to effect sealing of the overlapping arms of said strip.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Dillon Nov. 15, 1921 Sowter Mar. 15, 1955 Broske Mar. 19, 1957 Hammell July 23, 1957 6 Fuller July 29, 1958 Sowa Dec. 2, 1958 OTHER REFERENCES AMP pamphlet, received in Patent Office March 5, 1954 (page 3 relied on). 

